What is Degeneracy pressure: Definition and 23 Discussions

Degenerate matter is a highly dense state of fermionic matter in which the Pauli exclusion principle exerts significant pressure in addition to, or in lieu of thermal pressure. The description applies to matter composed of electrons, protons, neutrons or other fermions. The term is mainly used in astrophysics to refer to dense stellar objects where gravitational pressure is so extreme that quantum mechanical effects are significant. This type of matter is naturally found in stars in their final evolutionary states, such as white dwarfs and neutron stars, where thermal pressure alone is not enough to avoid gravitational collapse.
Degenerate matter is usually modelled as an ideal Fermi gas, an ensemble of non-interacting fermions. In a quantum mechanical description, particles limited to a finite volume may take only a discrete set of energies, called quantum states. The Pauli exclusion principle prevents identical fermions from occupying the same quantum state. At lowest total energy (when the thermal energy of the particles is negligible), all the lowest energy quantum states are filled. This state is referred to as full degeneracy. This degeneracy pressure remains non-zero even at absolute zero temperature. Adding particles or reducing the volume forces the particles into higher-energy quantum states. In this situation, a compression force is required, and is made manifest as a resisting pressure. The key feature is that this degeneracy pressure does not depend on the temperature but only on the density of the fermions. Degeneracy pressure keeps dense stars in equilibrium, independent of the thermal structure of the star.
A degenerate mass whose fermions have velocities close to the speed of light (particle energy larger than its rest mass energy) is called relativistic degenerate matter.
The concept of degenerate stars, stellar objects composed of degenerate matter, was originally developed in a joint effort between Arthur Eddington, Ralph Fowler and Arthur Milne. Eddington had suggested that the atoms in Sirius B were almost completely ionised and closely packed. Fowler described white dwarfs as composed of a gas of particles that became degenerate at low temperature. Milne proposed that degenerate matter is found in most of the nuclei of stars, not only in compact stars.

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  1. Ken G

    I Without degeneracy, when would Solar cores collapse?

    I believe I know the answer to this question, but it is still very informative to ask: Would iron stellar cores still collapse when they reached some mass without degeneracy (by which I mean, if electrons were not indistinguishable, so did not obey the Pauli exclusion principle on such large...
  2. G

    B Degeneracy Pressure: Pauli Principle & Neutron Stars

    Is degeneracy pressure created due to Pauli exclusion principle able to create some waves? Also at neutron star stage similarly are there waves created may be of higher energy? Can we talk of some harmonic motions in these stages?
  3. Kayla Martin

    Why is the degeneracy criterion the same for all stars?

    Is it anything to do with the equation being independent of mass etc.. of the star? or to do with the Pauli exclusion principle? Any help will be much appreciated.
  4. tanaygupta2000

    Degeneracy pressure of a White Dwarf Star

    So far, I am provided with all the required values for calculation, except N. If N = total number of electrons in star, then using N = mass of star/ mass of an electron should be no problem. Am I right?
  5. P

    I Neutron vs electron degeneracy pressure

    How is neutron degeneracy pressure able to support a much higher density object such as a neutron star where electron degeneracy pressure only supports a comparatively less dense object such as a white dwarf. Conceptually I would think electron degeneracy pressure to be stronger due to the...
  6. P

    B Why is there no proton degeneracy pressure?

    Hello. I usually heard about electron degeneracy pressure and neutron degeneracy pressure. But I´ve never heard about a proton degeneracy pressure. Why is this?
  7. S

    B Angular momentum, degeneracy pressure, and cosmic inflation

    Considering the angular momentum of a collapsing star preventing it from resulting in a black hole by degeneracy pressure, are there ekpyrotic universe models that include angular momentum and degeneracy pressure as key factors of cosmic inflation?
  8. Ranku

    I Electron degeneracy pressure

    Is Pauli Exclusion Principle alone responsible for electron degeneracy pressure?
  9. J

    B Neutron, White Dwarfs and Degeneracy Pressure

    Hi, I have been trying to get some physics behind the cause of the degeneracy pressure but have some confusion with the stuff I have found. Apparently the cause of degeneracy pressure can be explained through the uncertainty principle. If you trap electrons in a smaller and smaller space the...
  10. FallenApple

    I Electron Degeneracy Pressure not Fundamental?

    So for what I understand, when a star collapses, the electrons do not like to overlap their quantum states because of the pauli exlusion principle. Is this different from an E&M force? If so, then why isn't it a fundamental interaction? All forces are made of a combination of the 4 fundamental...
  11. B

    Degeneracy pressure and stellar collapse

    I have a question. In a massive star (more than say 5 times the mass of the sun), the electron/neutron degeneracy pressure is unable to prevent the gravitational collapse. Does this imply that the Pauli's exclusion principle breaks down and two or more electrons/neutrons collapse to the same...
  12. Helios

    Collapsars vrs. QM degeneracy pressure

    The QM degeneracy pressure puts up a fight but the immensity of the star wins out. Why is this? Is the Pauli Exclusion Principle really a principle? Why does it surrender in this case?
  13. Ken G

    Are there widespread misconceptions about degeneracy pressure?

    Two statements that are often made about degeneracy pressure are: 1) It is a new or special kind of pressure that requires quantum mechanics, in contrast with ideal gas pressure, which in effect involves somewhat mysterious forces that emerge from the Pauli exclusion principle, and 2) it...
  14. P

    Electron Degeneracy Pressure

    I have a question: is there any way to accurately "visualize" the phenomenon of electron degeneracy pressure? I understand that the main concept behind it is the Pauli Exclusion Principle. However, I was reading about the Chandrasekhar limit, and that it's derived from the fact that although a...
  15. K

    What is degeneracy pressure?

    Sorry for the noob question, but is there a resource anyone can point me to for an easy to understand explanation of degeneracy pressure? I have no scientific background at all, so when I say easy I'm not kidding, but I am looking for a bit more than the pop sci bit of the Wikipedia entry...
  16. J

    Did quantum degeneracy pressure drive inflation?

    Was cosmic inflation partly driven by the quantum degeneracy pressure of the quarks and electrons? Just after the Big Bang they would all be sitting on top of each other - just what fermions don't like to do!
  17. cepheid

    Gravity vs. Degeneracy Pressure

    Okay, I noticed that my OP got 39 views but no responses, so let me change my strategy. Here is my question: An object made out of degenerate matter (e.g. white dwarf) will collapse if more gravitational energy is lost in getting smaller than the energy that is gained due to electron...
  18. R

    Degeneracy pressure and interactions

    hi, I wonder if the electromagnetic force is the force that expresses how pressure interacts. I mean, a pressure is a force divided by a surface. is that force the electromagnetic force, that would be the consequence of an increased kinetic energy?
  19. N

    Electron degeneracy pressure in QM

    In BLACK HOLES AND TIME WARPS by Kip Thorne there is a fascinating discussion about how electron degeneracy pressure fights gravity in dense stars, beginning on page 146. He says the following (abbreviated excerpts) : "..Quantum mechanics insists that when already dense matter is compressed...
  20. L

    Which of the four forces is responsible for degeneracy pressure?

    Actually, i have two questions: 1. Because of the Pauli exclusion principle, there can be degeneracy pressure, for instance in neutron stars, but also in electron gasses (and any fermion cluster?). What force causes this pressure? 2. According to the Pauli Exclusion principle, no two...
  21. L

    What Causes Degeneracy Pressure?

    I was wondering something, a collection of fermions can resist compressing forces due to what is termed degeneracy pressure. I was wondering, which of the four fundamental interactions is this due to? Thanks. Molu
  22. CJames

    Neutron degeneracy pressure and electron degeneracy pressure

    The words neutron degeneracy pressure and electron degeneracy pressure are thrown around a lot when talk of white dwarfs, neutron stars, and black holes comes up. Despite this, I can't find a quantitative description of these critical pressures ANYWHERE. It is almost always described in terms of...
  23. K

    Neutron degeneracy pressure

    How can gravity overcome the degeneracy pressure of neutrons in a neutron star? Isn't such a thing the same as violating the uncertainty principle?